Conventionally, rimfire ammunition cartridges comprise a cylindrical casing usually of brass although other metals or alloys such as steel may be employed that is closed at one end and open at the other end, the open end being crimped to a bullet, usually of lead. The closed end or head of the casing defines an annular flange or rim containing a priming composition which ignites by a rimfire strike and the hollow body of the casing contains a propellant which is fired by the ignition of the primer causing raid expansion of hot gases to force the bullet from its seating.
The bullet conventionally has a cylindrical body portion, which may be solid or hollow and a tapered, curved portion leading from the cylindrical body to the nose of the bullet. The body portion usually has external knurls to hold lubricant which is provided to prevent material being stripped from the circumference of the bullet as it is expelled along the barrel of the gun.
It is especially desirable for target and sporting applications that ammunition cartridges of the same type perform consistently and reliably. Small variations from one cartridge to another can have a significant effect on the accuracy of the ammunition. Accordingly, there is a continuing desire to improve the accuracy of ammunition cartridges.